Pliers with automatic fulcrum shift



Sept. 29, 1959 w. s. MILLER PLIERS WITH AUTOMATIC FULCRUM SHIFT 2Sheets-Sheet 1 Filed Sept. 7, 1956 WENDELL S. ,M/LLEQ,

INVENTOR.

Sept. 29, 1959 w. s. MILLER PLIERS WITH AUTOMATIC FULCRUM SHIFT 2Sheets-Sheet 2 Nnwx xx w 745 7 NN m E WENDELL -51 .M/LLEQ.

United States Patent 2,906,155 PLIERS WITH AUTOMATIC FULCRUM SHIFTWendell S. Miller, Los Angeles, Calif. Application September 7, 1956,Serial No. 608,489 13 Claims. (Cl. 81-343) This invention relates toimproved pliers and similar hand tools, consisting of two pivotallyinterconnected elongated members having jaw portions at one end, and

handle portions at their opposite ends for actuating the jaws. Where theterm jaw is used in this application, it is contemplated these jaws maybe either gripping elements for tightly holding a work piece, or cuttingelements for cutting the work piece.

The general object of the invention is to provide a new type tool ofthis general character which is automatically adjustable to differentconditions for most effectively gripping or acting against dilferentsizes of work piece. More specifically, the tool acts by itself, andduring a closing operation, to shift from one condition to another at aproper time for most eifectively engaging the particular work piecebeing handled. During the initial portion of a closing movement, thejaws may close relatively rapidly in relation to movement of thehandles, but with little force. Then, after engagement with the workpiece, the tool may shift to a condition in which a much greater forceis applied to the jaws, with the handles automatically being adjusted,by said shifting of conditions, in a manner maintaining the handleswithin a desired range of movement when the work piece is actually beinggripped.

To achieve this automatic adjustment of the tool, the two sections ofthe tool are adapted to swing or pivot relative to one another abouteither of two different pivot points or axes. During the initial portionof a closing movement, the sections pivot about a first of these axes,which may be relatively far from the work engaging jaws; and then when awork piece is engaged by the jaws and resists further closing movement,the parts automatically adjust to a condition in which they pivot abouta second center which is closer to the jaws and work piece. The pivotalconnection at the first center may be constructed to slip transverselyof its axis when the work piece is engaged, and that slippage can thencam one of the two sections longitudinally in a manner rendering ashiftable pivot part near the jaws effective as a fulcrum element.

Certain particular and highly important features of the invention haveto do with the manner of construction of the first or primary pivotalconnection, that is, the connection which is effective during the firstpart of a closing operation. Specifically, this connection may include apivot pin which is carried by one of the two pivoted sections of thedevice, and which extends through' an elongated slot in the othersection. The pin is confined Within a predetermined end or portion ofthe slot during the first part of a closing operation, and then slipsfrom that location and along the slot when a work piece resists furtherclosure of the jaws. The slot is so shaped as to cam the two sectionslongitudinally relative to each other when the pin thus slips along theslot, to thereby render the second pivotal or swinging connectioneffective. When such a pin and slot connection is employed, the twomembers'can be very effectively held in assembled relation by merelyproviding a head on the pin at an outer side of the slot and of a sizeincapable of passing through the slot. Preferably, the pin is releasablyretained in its initial position in the slot by suitable yielding ordetent means, as by a suitable spring acting against the pin. In oneform of the invention, this spring detent 2,906,155 Patented Sept. 29,195$ will function also to releasably retain the pin against returningmovement toward its initial position after having been shiftedtherefrom, and until a user purposely releases the detent to allow suchreturning movement.

I The second pivotal connection may include a pivot part on one of thejaws which is engageable in any of different positions with a series ofteeth on the other jaw. This secondary pivot part may be a toothed lugon the associated jaw adapted to act as a fulcrum member when inengagement with the coacting series of teeth. As will be brought out,the range of required swinging movement of the two members about thesecond center is very small, and therefore this secondary pivot part orfulcrum member need not be designed to allow any extended range ofpivotal movement.

A further feature of the invention resides in the pre ferred positioningand formation of the holding teeth which are engaged by the secondarypivot part to form the secondary pivotal connection. Specifically, theseteeth may be formed on one of the jaw sections of the device, at alocation facing essentially toward the location at which a work piece isreceived between the jaws.

The above and other features and objects of the present invention willbe better understood from the following detailed description of thetypical embodiments illustrated 'in the accompanying drawings in which:

Fig. 1 is a side view of a pair of pliers constructed in accordance withthe invention, and showing the pliers in their fully open position;

Fig. 2 is a smaller view similar to Fig. l, but showing the pliers in agripping condition;

Fig. 3 is an enlarged fragmentary section taken on lin 3-3 of Fig. 2;

Fig. 4 is a fragmentary section taken on line 4--4 of Fig. 3;

Fig. 5 is a fragmentary section taken on line 5-5 of Fig. l;

Fig. 6 is a view corresponding to Fig. l, but showing a variational formof the invention;

Fig. 7 is a view showing the Fig. 6 device in its active gripping orcutting condition; V

Fig. 8 is a fragmentary section taken on line 88 of Fig. 6; and

Fig. 9 is a fragmentary section taken on line 9--9 of Fig. 6.

In the drawings, the tool 10 includes two elongated rigid metal members11 and 12, which have first handle ends 13 and 14 adapted to be actuatedtoward and away from each other, and second jaw ends 15 and 16 forgripping a work piece 17 in response to actuation of handle ends 13 and14. The jaws 15 and 16 of course may be provided with the usualirregularities or teeth 18, for assuring effective grippingof the workpiece. The two handle ends 13 and 14 are so relatively positioned as tobe receivable within the hand of a user, to be manually actuated towardand away from each other in the manner of conventional pliers. v

Member 12 rigidly carries a pivot pin 19, which preferably extendsdirectly transversely of members 11 and 12, and whose reducedcylindrical portion 119 may be a tight pressed fit within an opening 120in member 12. Portion 119 of the pin projects transversely beyond member12, and is movably received within a slot 20 formed in a somewhatenlarged portion 11a of member 11, the slot having a width which is onlyslightly larger than the diameter of a bearing sleeve 219 received aboutpin portion 119. At its opposite ends, pin 19 may have a pair ofenlarged circular heads 21 and 121; and between head 21 and portion 119,pin 19 may have an intermediate size cylindrical portion 122. Thediameters of portion 122 and 21 and 121 are all greater than the widthofslot 20 and the diameter of opening 120, so that 3 members 11 and 12are at all times confined between portions 122 and 121 of the pin, toretain members 11 and 12 in assembled condition.

Slot 20 has an end portion 22 which curves-in a direction away from thejaw end 15 of part 11, and which forms a partial cylindrical bearingsurface at the end of the slot for engaging bearing sleeve 219 on pin 19in the Fig. 1 condition of the tool, to form with pin 19 and its sleeve219 a pivotal connection attaching parts 11 and 12 together for relativeswinging or pivotal movement about the axis of pin 19. The pin isyieldingly retained in the illustrated Fig. 1 position within the endportion 22 of slot 20 by means of a spring 23, one of whose ends 123 isretained in fixed relation to member 11, as by reception within atransverse slot 124 formed in a pin 111 (the spring end typically beinga tight pressed fit in slot 124). The spring has a coiled portion 125,extending about pin 111, and then projects past pin 19, in engagementwith its enlarged portion 122, to yieldingly hold the pin within end 22of the slot. Except at its turned end 22, slot 20 extends arcuatelyabout essentially the location of a secondary pivot part 25 which iscarried by member 11 near its jaw end, and which will be discussed ingreater detail at a later point. Upon movement of pin 19 from end 22 ofslot 20, toward its opposite end, spring 23 is yieldingly deflected, asto the position of Fig. 2.

Member 12 has near its jaw end 18 a laterally enlarged portion 27, whichcarries an arcuate series of teeth 28 facing essentially toward the jawend of member 12 and centered about the axis of pin 19. The previouslymentioned pivot part 25 carried by member 11 has a series of similarteeth 29 which are engageable with teeth 28 by longitudinal shiftingmovement of member 11 relative to member 12, and which act to preventrelative pivotal movement of members 11 and 12 about the axis of pin 19when teeth 29 are engaged with teeth 28. Pivot part 25 may typically beformed as an integral lug or projection on member 11, and may have aside shoulder engageable at 30 with an end projection 31 on ing movementof jaws 15 and 16 at the Fig. 1 position.

Also, lug 25 may have a portion 125 projecting to a position overlyingthe toothed portion 28 of part 12, to assist -in retaining parts 11 and12 against one another.

As long as teeth 29 and 28 are not engaged, members 11 and 12 can pivotfreely about pin 19.

To now describe the operation of the device, assume that it is desiredto grip the work piece 17 between jaws 15 and 16 of tool 10. In order toperform this operation, the user first places part 17 between the jaws,and then commences to manually actuate handle elements 13 and 14relatively together. During the first portion of the movement of handles13 and 14 toward one another, these handles and the rest of parts 11 and12 pivot freely about the axis of pin 19, which is then received withinthe end portion 22 of slot 20. During such initial pivotal movement,pivot part 25 is held out of engagement with teeth 28, thus permittingfree swinging movement of the jaw ends about pin 19.

When the pivotal closing movement has reached the point at which jaws 15and 16 engage opposite sides of work piece 17, the work piece resistsfurther closing movement of the jaws, and therefore any further closingmovement of handles 13 and 14 will cause pin 19 and its bushing 219 tobe displaced from end portion 22 of slot 20, against the tendency ofspring 23, and to then progressively move along slot 20 toward itsopposite end. Since the end portion 22 of slot 20 is curved away fromthe jaw end of member 11, the wall of the slot forms a curving camsurface at 32, whose engagement with bushing 219 acts to progressivelycam member 11 longitudinally relative to pin 19 as the pin slips out ofend portion 22 of slot 20 and into its arcuate portions 26. Thislongitudinal camming movement of member 11 is just .sufiicient to movethe teeth 29 of pivot part 25 into meshing engagement with teeth 28 ofmember 12, to prevent further closing movement of pivot part 25 relativeto teeth 28.

After part 25 has thus been moved into engagement with teeth 28, anyfurther relative closing movement of members 11 and 12 must be aboutessentially the pivot part 25 as a pivotal axis or fulcrum. Thus, thepivotal connection between members 11 and 12 is automatically moved fromthe location of pin 19 to the location of pivot part 25, in response toengagement of jaws 15 and 16 with work piece 17. Upon further closure ofhandles 13 and 14, the jaws move very slowly as compared with themovement of the handles, but with great force or leverage being appliedagainst the work piece. In order to allow for the necessary pivotalmovement of members 11 and 12 about pivot part 25, the teeth 29 of part25 may extend along an essentially curved path, which is curvedoppositely to the arcuate curvature of teeth 28, the teeth 29 typicallybeing curved about an axis represented at 33. Thus, during therelatively slight pivotal movement about part 25, the teeth 29 arecapable of rolling slightly along teeth 38, to permit the specifiedpivotal movement. After the gripping operation is completed, handles 13and 14 may be moved sufficiently far apart to return part 19 into end 22of slot 20, in preparation for the next gripping action. As will beapparent, the device is operative in the discussed manner to grip workpieces of any desired size, and regardless of the size of the piece, thejaws will pivot about pin 19 until the work piece is contacted, and willthen automatically shift to a condition in which they pivot essentiallyabout part 25, for increased gripping force in an automatically adjustedcondition.

Figs. 6 to 9 show a tool which is essentially very similar to that ofFigs. 1 to 5, differing only in the respects discussed specifically inthe following description. This Fig. 6 tool 10a includes two elongatedrigid members 11a and 12a, having handle ends 13a and 14a, and jaw ends15a and 16a. In this case, the jaws 15a and 16a have typically beenrepresented as being cutter blades rather than gripping jaws, the bladeshaving sharp cutting edges at 18:: for cutting into or through a workpiece. The member 12a carries a pivot pin 19a which is received withinan end portion 22a of an arcuate slot 20a centered essentially aboutpivot part 25a. Pin 19a and its bushing 219a are yieldingly retainedwithin the end portion 22a of slot 20a by means of a detent element 23awhich is formed of a single elongated piece of spring wire bent to theillustrated configuration. This spring has a first U-shaped or doubledback portion 300 which is received and held in fixed position within aslot 301 in member 11a. Beyond portion 300, wire 23a has a secondU-shaped portion 302, which extends parallel to and adjacent to theouter surface 303 of part 11a, and which normally returns to theposition of Fig. 6 across the path of pin 21 of bushing 219a. At itsouter end, wire 23a has a portion 304 projecting transversely away frompart 11a, and carrying a loop 305 by which the U-shaped portion 302 maybe manually retractable to the broken line position of Fig. 6.

Pin 19a can only move into the arcuate portion of slot 20a by deflectionof portion 302 of part 23a to this broken line position; and after pin19a moves past detent 23a, the latter resiliently returns to the Fig. 6full line position to prevent return of pin 19a past the detent untilthe detent is manually released to the broken line position by movementof loop 305.

As seen clearly in Fig. 6, the end portion 22a of slot 20a correspondsto portion 22 of slot 20, except that in Fig. 6 the end portion of theslot curves toward the jaw end 15a of member 11a, rather than toward itshandle end as in Fig. 1. Thus, the member 11a is shifted longitudinallytoward its jaw end, rather than its handle end, when pin 19a moves outof the end portion 22a of the slot. In order to render pivot part,25aeffective as a fulcrum element upon such longitudinal shifting of member11a, the teeth 29a on pivot part 25a, and the arcuate series of teeth28a on member 12a, face in opposite directions than in Fig. 1. Pivotpart 25a may be received within an essentially arcuate slot 31a, so thatswinging movement of pivot part 25a is limited by engagement of thatpart with the ends of the slot. Also, in Fig. 6, the pivot part istypically shown as being pivotally mounted about a pin 125a, which isrigidly attached to member 11a. The arcuate series of teeth 28a may becentered about the axis of pin 19a, and the teeth 29a may be centeredabout that axis when pivot part 25a is in its Fig. 6 position. The pin125a about which part 25a is received may of course. have a suitableenlarged head represented at 225a for holding part 25a againstseparation from member 11a. Also, the pivot part 25a may have an arcuatesurface 225a centered about the axis of pin 19a, and slideablyengageable with an arcuate correspondingly centered surface 226a onmember 12a (at the inner side of slot 31a) to hold the pivot part 25aagainst turning movement relative to part 12a from the illustratedproperly oriented position.

In using the Fig. 6 device, pin 19a remains within end 22a of slot 20aduring the initial closing movement of handles 13a and 14a and cuttingjaws 15a and 16a. When the jaws engage a work piece, the resistanceoffered by that work piece causes pin 19aand its bushing 219 to deflectdetent element 23a and move into the elongated arcuate portion of slota, with the pin and member 11a being cammed longitudinally by virtue ofthe engagement of the bushing 219 with cam surface 122a. Thislongitudinal movement of member 11a moves pivot part 25a into engagementwith teeth 28a, so that thereafter the members 110 and 120 are hinged atpivot part 25a rather than the pin 19a, to increase the leverage exertedagainst the work piece. This allows the user to apply a relatively greatcutting force to the work piece through blades 15a and 16a, though ofcourse the blades will not normally close on a single actuation.Repeated cutting actions may be effected in this manner, with the tooleach time automatically adjusting the jaws to a slightly more closedcondition before pivot part 25a moves to active position, so that thecutting actions may progressively cut deeper and deeper through the workpiece. After each cutting action, the detent part 23a is of coursemanually released to permit return of pin 1901 to its Fig. 6 position.

I claim:

1. A plier type tool comprising two elongated rigid relatively pivotablemembers having handles at their first ends movable toward and away fromeach other and having jaws at their opposite ends actuable toward andaway from each other and against a work piece by said movement of thehandle ends, a first of said members containing a slot between saidhandle and jaw ends thereof, a pivot pin on the second member receivedwithin an end of said slot during initial closing movement of themembers and thereby forming a first pivotal connection between themembers, said slot extending in a direction to permit passage of saidpin along the slot and away from said end of the slot when a work pieceresists closing movement of the jaws, said pivot pin be- .ing secured tosaid first member against separation therefrom and having an enlargedhead at an outer side of said slot and wider than the slot to hold saidtwo members together, said slot being defined by a pair of spaced .edgesurfaces extending along opposite sides of the slot and engageable withopposite sides of said pin to confine it for movement along the slot,one of said edge surfaces being shaped to cam'said pin in a direction toshift said second member generally longitudinally relative to said firstmember in response to said movement of the pin from said end of theslot, an additional pivot cai'r'ied by one of the members at a locationcloser to its jaw end than is said first pivotal connection and movablein a closing direction relative to the other member during said initialclosing movement of the jaws, and an arcuate series of teeth on saidother member engageable with said additional pivot part in response tosaid relative camming of the members by the slot and pin and operable tothen form with said pivot part a second connection interconnecting saidmembers for relative swinging movement about a location closer to thejaws than is said first connection, said slot having an essentiallyarcuate portion along which said pin moves after the pin shifts fromsaid end of the slot.

2. A plier type tool comprising two elongated rigid.

relatively pivotable members having handles at their first ends movabletoward and away from each other and having jaws at their opposite endsactuable toward and away from each other and against a work piece bysaid movement of the handle ends, a first of said members containing aslot between said handle and jaw ends thereof, a pivot pin on the secondmember received within an end of said slot during initial closingmovement of the members and thereby forming a first pivotal connectionbetween the members, said slot extending in a direction to permitpassage of said pin along the slot and away from said end of the slotwhen a work piece resists closing movement of the jaws, said pivot pinbeing secured to said first member against separation therefrom andhaving an enlarged head at an outer side of said slot and wider than theslot to hold said two members together, said slot being defined by apair of spaced edge surfaces extending along opposite sides of the slotand engageable with opposite sides of said pin to confine it formovement along the slot, one of said edge surfaces being shaped to camsaid pin in a direction to shift said second member generallylongitudinally relative to said first member in response to saidmovement of the pin from said end of the slot, an additional pivot partcarried by one of the members at a location closer to its jaw end thanis said first pivotal connection and movable in a closing directionrelative to the other member during said initial closing movement of thejaws, an arcuate series of teeth on said other member engageable withsaid additional pivot part in response to said relative camming of themembers by the slot and pin and operable to then form with said pivotpart a second connection interconnecting said members for relativeswinging movement about a location closer to the jaws than is said firstconnection, said slot having an essentially arcuate portion along whichsaid pin moves after the pin shifts from said end of the slot, and meanspivotally attaching said pivot part to said one member, said othermember containing an arcuate slot within which said pivot part isreceived and having at one of its sides an arcuate series of teethengageable in holding relation and in different positions with saidpivot part, said last mentioned slot having along a second of its sidesanarcuate guide surface slidably engaging a surface on said pivot partto hold it in predetermined relation to said other member.

3. A plier type tool comprising two elongated rigid relatively pivotablemembers having handles at their first ends movable toward and away fromeach other and having jaws at their opposite ends actuable toward andaway from each other and against a workpiece by said movement of thehandle ends, a first of said members containing a slot between saidhandle and jaw ends thereof, a pivot pin on the second member receivedwithin a predetermined portion of said slot during initial closingmovement of the members and thereby forming a first pivotal connectionbetween the members, said slot extending in a direction to permitpassage of said pin along the slot and away from said predeterminedportion of the slot when a work piece resists closing movement of thejaws, said slot being defined by a pair of spaced edge surfacesextending along opposite sides of the slot and engageable with oppositesides of said .pin to confine it for movement along the slot, one ofsaid edge surfaces being shaped to cam said pin in a direction to shiftsaid second member generally longitudinally relative to said firstmember in response to said movement of the pin along the slot and awayfrom said predetermined portion of the slot, an additional .pivot partcarried by one of the members at a location closer to its jaw end thanis said first pivotal connection and movable in a closing directionrelative to the other member during said initial closing movement of thejaws, holding means on said other member engageable with said additionalpivot part in response to said relative camming of the members by theslot and pin and operable to then form with said pivot part a secondconnection interconnecting said members for relative swinging movementabout a location closer to the jaws than is said first connection, and aspring detent unit yieldingly retaining said pin in said predeterminedportion of the slot until the jaws engage a work piece and thendeflectible to permit passage of the pin along the slot to effect saidlongitudinal camming of said second member, said spring unit then beingoperable to releasably hold said pin against returning movement to itsinitial position in said predetermined portion of the slot.

4. A plier type tool comprising two elongated rigid relatively pivotablemembers having handles at their first ends movable toward and away fromeach other and having jaws at their opposite ends actuable toward andaway from each other and against a work piece by said movement of thehandle ends, a first of said mem- .bers containing a slot between saidhandle and jaw ends thereof, a pivot pin on the second member receivedwithin a predetermined portion of said slot during initial closingmovement of the members and thereby forming a first pivotal connectionbetween the members, said slot extending in a direction to permitpassage of said pin along the slot and away from said predeterminedportion of the slot when a work piece resists closing movement of thejaws, said slot being defined by a pair of spaced edge surfacesextending along opposite sides of the slot and engageable with oppositesides of said pin to confine it for movement along the slot, one of saidedge surfaces being shaped to cam said pin in a direction to shift saidsecond member generally longitudinally relative to said first member inresponse to said movement of the pin along the slot and away from saidpredetermined portion of the slot, an additional pivot part carried bysaid first member at a location closer to its jaw end than is said firstpivotal connection and movable in a closing direction relative to thesecond member during said initial closing movement of the jaws, andholding means on said second member engageable with said additionalpivot part in response to said relative camming of the members by theslot and pin and operable to then form with said pivot part a secondconnection interconnecting said members for relative swinging movementabout a location closer to the jaws than is said first connection, saidpivot pin having a head at an outer side of said slot and projectinglaterally beyond at least one of said edge surfaces of the slot andoverlying a portion of said first member adjacent the slot to hold saidtwo members together.

5. A plier type tool as recited in claim 4, including means yieldinglyretaining said pin in said predetermined portion of the slot until thejaws engage a work piece.

6. A plier type tool as recited in claim 4, including a springyieldingly resisting said movement of the pin along the slot from saidpredetermined portion thereof and continuously urging said pin backtoward said predetermined portion of the slot after displacementtherefrom.

7. A plier type tool as recited in claim 4, in which said holding meanscomprise a series of teeth carried by said 8 second member andengageable with said pivot part in holding relation in any of differentpositions.

8. A plier type tool as recited in claim 4, in which said holding meanscomprise a series of teeth on said second member engageable with saidpivot part in any of different positions, there being means pivotallyat- .taching said pivot part to said first member.

9. A plier type tool as recited in claim 4, in which said holding meanscomprise a series of teeth on said second membenand said pivot part isan integral lug on said first member rigidly fixed relative thereto andengageable in holding relation and in different positions with saidfirst mentioned teeth.

10. A plier type tool as recited in claim 4, in which said second membercontains an arcuate slot within which said pivot part is received andarcuately movable, said holding means comprising an arcuate series ofteeth formed along a side of said last mentioned slot and engageablewith said pivot part in holding relation.

11. A plier type tool as recited in claim 4, including a spring detentelement formed of a resilient wire attached at one point to said firstmember and constructed to yieldingly resist movement of the pin alongthe slot between said predetermined portion thereof and the rest of theslot, said detent element having a portion projecting to a locationaccessible to a users hand and adapted to be moved by said hand, andadapted by said movement to release the detent to permit movement of thepin between said predetermined portion of the slot and the rest of theslot.

12. A plier type tool comprising two elongated rigid relativelypivotable members having handles at their first ends movable toward andaway from each other and having jaws at their opposite ends actuabletoward and away from each other and against a work piece by saidmovement of the handle ends, a first of said members containing a slotbetween said handle and jaw ends thereof, a pivot pin on the secondmember received within a predetermined portion of said slot duringinitial closing movement of the members and thereby forming a firstpivotal connection between the members, said slot extending in adirection to permit passage of said pin along the slot and away fromsaid predetermined portion of the slot when a work piece resists closingmovement of the jaws, said slot being defined by a pair of spaced edgesurfaces extending along opposite sides of the slot and engageable withopposite sides of said pin to confine it for movement along the slot,one of said edge surfaces being shaped to cam said pin in a direction toshift said second member generally longitudinally relative to said firstmember in response to said movement of the pin along the slot and awayfrom said predetermined portion of the slot, an additional pivot partcarried by said first member at a location near its jaw end and movablein a closing direction relative to the other member during said initialclosing movement of the jaws, and a series of teeth formed on saidsecond member and facing essentially away from said slot and toward thespace between said jaws and positioned to be engaged by said additionalpivot part in response to said relative camming of the members by theslot and pin and operable to then form with said additional pivot part asecond connection interconnecting said members for relative swingingmovement about a location closer to the jaws than is said firstconnection.

13. A plier type tool as recited in claim 12, in which said pivot partis a lug on said first member stationarily and rigidly fixed relativethereto and having teeth engageable with said first mentioned teeth indifferent positions, said first mentioned series of teeth being arcuateand centered essentially about said pin.

References Cited in the file of this patent UNITED STATES PATENTS1,651,216 McGill Nov. 29, 1927

